**Exhibit 31(a)****CERTIFICATION**I, William J. Doyle, certify that:     1. I have reviewed this Annual Report on Form 10-K ofPotash Corporation of Saskatchewan Inc.;     2. Based on my knowledge, this report does not contain anyuntrue statement of a material fact or omit to state a materialfact necessary to make the statements made, in light of thecircumstances under which such statements were made, notmisleading with respect to the period covered by this report;     3. Based on my knowledge, the financial statements, andother financial information included in this report, fairlypresent in all material respects the financial condition,results of operations and cash flows of the registrant as of,and for, the periods presented in this report;     4. The registrant’s other certifying officer and I areresponsible for establishing and maintaining disclosure controlsand procedures (as defined in Exchange Act Rules 13a-15(e)and 15d-15(e)) and internal control over financial reporting (asdefined in Exchange Act Rules 13a-15(f) and 15d-15(f)) forthe registrant and have:          (a) designed such disclosure controls and procedures, or caused    such disclosure controls and procedures to be designed under our    supervision, to ensure that material information relating to the    registrant, including its consolidated subsidiaries, is made    known to us by others within those entities, particularly during    the period in which this report is being prepared;           (b) designed such internal control over financial reporting, or    caused such internal control over financial reporting to be    designed under our supervision, to provide reasonable assurance    regarding the reliability of financial reporting and the    preparation of financial statements for external purposes in    accordance with generally accepted accounting principles;           (c) evaluated the effectiveness of the registrant’s    disclosure controls and procedures and presented in this report    our conclusions about the effectiveness of the disclosure    controls and procedures, as of the end of the period covered by    this report based on such evaluation; and           (d) disclosed in this report any change in the registrant’s    internal control over financial reporting that occurred during    the registrant’s most recent fiscal quarter (the    registrant’s fourth fiscal quarter in the case of an annual    report) that has materially affected, or is reasonably likely to    materially affect, the registrant’s internal control over    financial reporting; and     5. The registrant’s other certifying officer and Ihave disclosed, based on our most recent evaluation of internalcontrol over financial reporting, to the registrant’sauditors and the audit committee of the registrant’s boardof directors (or persons performing the equivalent functions):          (a) all significant deficiencies and material weaknesses in the    design or operation of internal control over financial reporting    which are reasonably likely to adversely affect the    registrant’s ability to record, process, summarize and    report financial information; and           (b) any fraud, whether or not material, that involves management    or other employees who have a significant role in the    registrant’s internal control over financial reporting.Date: March 11, 2005           By:     /s/ WILLIAM J. DOYLE             William J. Doyle    *President and Chief Executive Officer*